Most deposits are shallow, maybe 60m, generally easy to mine with conventional drill, blast, load & haul techniques, normally a low strip ratio because the deposits are near surface. Pits are normally fairly small in size because you have to be selective, lots of benches, GRADE CONTROL is the #1 name of the game. Almost becomes detailed earthworks not bulk mining (not quite but it's nothing like open cut iron ore mining for example). And can be huge in size, but very low grade 1-2% at best.
Saprolite and limonite clays contain the highest grade ore.
Mt Keith is the biggest deposit in Australia. Low grade, but LOTS of the ore.
So whoever is the proponent that you are interested in, the mine planning department is the key. If that is stuffed up, then forget it. You would want to suss out who they have on staff.
High pressure acid leach or open air heap leach can be used depending on the ore type. Difficult to process the ore. A variety of nasty chemicals are required within the process plant to leach the ore. Sulphuric acid, sulphur dioxide, sulphur trioxide, hydrogen sulphide, ammonia, hydrogen peroxide, hydrogen, oxygen, nitrogen - that about covers it.
That's just to get to a mixed hydroxide product Ni and Co. If you want to refine it then there is sintering plant etc required on top of that. Cobalt is carcinogenic. Nickel oxide dust isn't very good for one's health either, let alone all the chemicals within the plant.
Biggest input costs are the sulphur (for sulphuric acid production) and a very energy hungry plant (creating H2SO4 is exothermic so plants capture the heat and generate steam for turbines but still use an enormous amount of energy).
Tailings are highly acidic and have to be neutralised before being disposed of. Usually by being mixed with Calcrete, Limestone or similar.
It costs a bomb to construct and operate a plant. There have been many places that have fallen over. Billions have been lost......
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